Housing for an electromagnetic relay

ABSTRACT

A small electromagnetic relay in which an electromagnet (116), having at least a core (130), a coil bobbin (128) and an armature (117), is accommodated in a box-shaped insulated housing (110) which has surrounding walls (114a, 114b) to hold contact terminals (111a, 111b, 112a, 112b), the electromagnet having an accommodation portion that is molded on the outer surface of a flange (138) of the coil bobbin as a unitary structure to rotatably hold the armature, the coil bobbin being equipped with the armature and the core.

DESCRIPTION BACKGROUND OF THE INVENTION

The present invention relates to a thin, small relay which is mountedchiefly on printed boards. Especially, the invention relates to anelectromagnetic relay of the construction in which an electromagnet,having at least a core, a coil and an armature, is accommodated in abox-like insulated housing which has surrounding walls to hold terminalsof fixed and moving contacts, and to a method of manufacturing the same.

FIG. 1 is a perspective view of a conventional small electromagneticrelay (hereinafter simply referred to as a relay), and FIG. 2 is aperspective view illustrating the relay of FIG. 1 in a disassembledmanner. In these drawings, reference numeral 10 denotes a support membercomposed of an insulating material which forms a rectangular box withits upper side being open and the bottom being closed. The opposing sidewalls 11 of the support member 10 have through holes 12 in whichterminals will be inserted. The side walls 11, further, have projections13 for fastening a moving contact spring member on the upper surfacesthereof, and projections 15 for securing a yoke plate in the recessedportions 14. A side wall 16 has a slit or slot 17.

Reference numerals 20, 20', 21, and 21' denote fixed contact terminals,22 and 22' denote coil terminals, and 23, 23' denote terminals for leadcontacts. These terminals have at their lower ends escape-preventingpieces 24 that fold after the terminals are inserted in the throughholes 12 of the side walls 11. The fixed contact terminals 20(21) and20'(21') have a difference in height at the contact points 25. Movingcontact springs, which will be mentioned later, are disposed between thecontacts 25 to form transfer contacts.

Reference numeral 30 denotes an electromagnet consisting of a core 32 onwhich a coil 31 is wound, an L-shaped yoke plate 33, and an L-shapedarmature 34. Lead wires of the coil 31 are wound on connection portions26 of coil terminals 22, 22' and are soldered. The core 32 is fastenedby caulking at one end to the yoke plate 33; the other end of the core32 works as an attracting portion 35 to attract the armature 34. Theyoke plate 33 has projections 37 with holes 36 on both sides thereof,and the armature 34 has a drive piece 38 for engaging a moving contactspring member and a projection 39 in the narrow portion thereof.Reference numeral 40 denotes a moving contact spring member having apair of moving contact springs 41 with one end of each spring 41 beingfastened to a molded member 42.

Each of the moving contact springs 41 is slightly bent. One end of eachcontact spring 41 has contacts 43, 43' on the front and back surfaces tocome into contact with the fixed contacts 20(21) and 20'(21'), and theother end has a connection piece 45 that is directly soldered toconnection portion 27 of the terminal 23 or 23' for the lead contact. Amolded insulator 44 is provided at the central portion of each contactspring 41. The molded member 42 has, on both sides, holes 46 into whichthe projections 13 are inserted. Reference numeral 50 denotes a releaseleaf spring which also works to prevent the armature 34 from escaping,and which consists of an L-shaped spring piece 52 having a hole 51 inone end thereof, and insertion pieces 54 with rising portion 53, whichare formed as a unitary structure. Reference numeral 60 denotes atransparent relay cover.

How the above-mentioned relay is assembled is described below. In therelay, the individual members are all mounted through the openings ofthe support member 10. That is, fixed contact terminals 20, 20', 21,21', coil terminals 22 and 22', and contact lead terminals 23, 23' areinserted in the through holes 12 of the support member 10, and aresecured by escape-preventing pieces 24. The electromagnet 30 is disposedin the housing with the core 32 on the lower side and the yoke plate 33on the side of the opening, whereby projections 37 and holes 36 arefitted into the recessed portions 14 and projections 15. The armature 34is inserted between one end a of the yoke plate 33 and the side wall 16,with the drive piece 38 disposed on the yoke plate 33, such that one enda is brought into agreement with the folded portion b of the armature34. Under this condition, the armature 34 faces the attracting portion35, and the folded portion b is folded at an angle that is slightlygreater than 90°, so that a gap is formed relative to the attractingportion 35.

The release leaf spring 50 is inserted in the slit 17 and is allowed tostay therein utilizing the resilient force of the rising portion 53. Thespring piece 52 of the release leaf spring 50 is positioned on thearmature 34, so that the projection 39 is fitted into the hole 51.

In the moving contact spring assembly 40, projections 13 are fitted intothe holes 46 to place the molded member 42 on the side walls 11, withthe moving contact springs 41 of the moving contact spring assembly 40being interposed between the fixed contact 20(21) and the fixed contact20'(21'), and with the insulator 44 being placed on the drive piece 38.Thereafter, projections 13, 15 protruding through holes 36, 46 areheated and caulked so that yoke plate 33 and the moving contact springassembly 40 become attached to the side walls 11 of the support member10. At the same time, the lead wires of the coil 31 are wound andsoldered onto the connection portions 26, and the connection portions 27are soldered to the connection pieces 45. Finally, the relay cover 60 ismounted on the support member 10 to produce the relay.

In the above-mentioned relay, the moving contact springs 41 areelectrically connected to the fixed contact terminal 20'(21') when theelectromagnet is not being excited. When the electromagnet 30 isexcited, the armature 34 is attracted to the attracting portion 35,whereby the drive piece 38 pushes the moving contact springs 41 up viathe insulator 44; the moving contact springs 41 come into contact withthe fixed contact terminals 20(21) to switch the contact.

In the above-mentioned conventional relay, however, the followinginconveniences occur, since electromagnet 30, moving contact springmember 40, release leaf spring 50, and contact spring terminals 20, 20',21, 21' are successively mounted into the box-shaped housing 10 which isformed by molding and which is composed of an insulating resin.

(1) A lot of assembling steps are necessary to manufacture a relay,requiring extended periods of time and a long assembly line.

(2) The assembling operation becomes cumbersome as the assemblingoperation proceeds. Therefore, parts tend to be deformed, and it becomesdifficult to produce relays with a high degree of reliability.

(3) So many parts are assembled in the housing that the above-mentioneddefects (1) and (2) become conspicuous, particularly when relays of asmall size are constructed. Accordingly, reducing the size of the relaycannot be achieved.

SUMMARY OF THE INVENTION

In order to solve the aforementioned problems inherent in theconventional relays, the present invention deals with a relay in whichan electromagnet is accommodated in a box-shaped housing which hassurrounding walls to hold contact spring terminals, wherein a portionfor accommodating an armature is integrally formed on the outer surfaceof the flange of the coil bobbin that is employed for the electromagnet,and the contact spring terminals are attached to the surrounding wallsof the box-shaped housing by insertion-molding. Owing to this idea, theobject of the present invention is to provide a relay which can beassembled efficiently and easily, within a short period of time andusing a reduced number of parts, which can therefore be economicallyproduced, and which has a reduced thickness and is small in size, and toprovide a method of manufacturing the same.

The present invention is concerned with an electromagnetic relay inwhich an electromagnet, having at least a core, a coil bobbin on whichthe coil is wound and an armature, is accommodated in a box-shapedinsulated housing which has surrounding walls to hold fixed contactterminals and moving contact spring terminals, wherein the outer surfacethe coil bobbin is equipped with a flange having a portion which ismolded as a unitary structure together with the coil bobbin and whichrotatably holds the armature, and wherein the armature and the core aremounted on the coil bobbin.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a conventional relay;

FIG. 2 is an exploded perspective view showing the relay of FIG. 1;

FIG. 3 is a perspective view showing a relay according to an embodimentof the present invention;

FIG. 4 is a side view showing, partly in cross section, of the relay ofFIG. 3;

FIG. 5 is an exploded perspective view showing parts which constitutethe relay of FIG. 3;

FIG. 6 is a perspective view showing lead frames used for the relay ofFIG. 3;

FIG. 7 is a perspective view showing an insertion-molded base whichincludes the lead frames of FIG. 6;

FIG. 8 is a perspective view schematically illustrating the facility forproducing the insertion-molded base of FIG. 7;

FIG. 9 is a sectional view of the insertion-molded base in which contactlead terminals are properly inserted;

FIG. 10 is a sectional view of the insertion-molded base in which thecontact lead terminals are inserted in a bent manner;

FIGS. 11A and 11B are a front view and a side view, respectively,illustrating an improved lead frame;

FIG. 12 is a sectional view showing an insertion-molded base in whichthe lead frame of FIG. 11 is inserted;

FIGS. 13A and 13B are a front view and a side view, respectively,showing another improved lead frame;

FIG. 14 is a sectional view of an insertion-molded base in which thelead frame of FIG. 13 is inserted;

FIGS. 15A and 15B are perspective views illustrating the steps forassembling the electromagnet;

FIGS. 16A and 16B are a plan view and a side view, respectively, showinga magnetic member which is used for forming a core;

FIG. 17 is a perspective view of a core formed by using the magneticmember of FIG. 16;

FIGS. 18A and 18B are a plan view and a side view, respectively, showinganother magnetic member for forming a core; and

FIG. 19 is a perspective view of a core formed by using the magneticmember of FIG. 18.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention will be described below inconjunction with the drawings. FIGS. 3 and 4 are a perspective view anda side view, respectively, illustrating the state in which a relay cover101 is removed from the relay of the embodiment of the presentinvention. In FIG. 3, reference numeral 110 denotes a box-like housingwhich is formed by molding an insulating material, such as syntheticresin, and which is open in both the upper and lower surfaces; 111a and111b denote fixed contact terminals on the "making" side; 112a and 112bdenote fixed contact terminals on the "breaking" side; and 113a and 113bdenote terminals for mounting moving contacts. These fixed contactterminals 111a, 111b, 112a, 112b, and moving contact-mounting terminals113a, 113b, are insertion-molded in opposing side walls 114a and 114b ofthe housing 110. The fixed contact terminals 111a, 111b, 112a, 112b, andmoving contact-mounting terminals 113a, 113b have terminal portions111a', 111b', 112a', 112b', 113a', and 113b' for connection to externalcircuits. FIG. 3, however, does not show terminal portions 111b', 112b',113b'. Contact portion 111a" (or 111b") of the fixed contact terminal111a (or 111b) and contact portion 112a" (or 112b") of the fixed contactterminal 112a (or 112b) have a difference in height, and a movingcontact spring 115a (or 115b) is disposed between the contact portion111a" (or 111b") and the contact portion 112a" (or 112b") to form atransfer contact. The rear ends of the moving contact springs 115a and115b are welded to the terminals 113a and 113b for mounting the movingcontacts. Further, the moving contact springs 115a and 115b are urgedtoward the fixed contact terminals 112a and 112b on the breaking side.When the electromagnet 116 is not energized, therefore, the movingcontacts 115a and 115b are electrically contacted to the fixed contactterminals 112a and 112 b on the breaking side.

The housing 110 contains the electromagnet 116. FIG. 3 shows an armature117 of the electromagnet 116, an armature-holding spring 118, coilterminals 119a, 119b, and an insulator 120 attached to an end of thearmature 117 that pushes up the moving contact springs 115a, 115b.Protrusions 121a, 121b are formed on the central upper portions of theopposing side walls 114a, 114b of the housing 110 to hold in positionthe electromagnet that is inserted through the lower opening of thehousing 110. Protrusions 122a, 122b are further formed in the vicinityof the protrusions 121a, 121b, so as to be fitted to the recessedportions (not shown) of a relay cover 101, such that the relay cover isfirmly fastened to the housing 110. FIG. 3 does not illustrateprotrusions 121b, 122b.

The relay cover 101 is formed by molding an insulating material, such asa transparent synthetic resin. A separator wall 102 for separating thecontacts is formed on the inner side of the relay cover 101 so that itis disposed between the side having fixed contact terminals 111a, 112aand the side having fixed contact terminals 111b, 112b, therebyincreasing the voltage isolation among the terminals. A protrusion 103is formed at a corner of the relay cover 101. The protrusion 103 will becut off after the relay is assembled, mounted on a printed board by thedipping of solder, and washed to remove solder flux; i.e., a ventilationport is formed in the relay cover 101 to radiate the heat.

As shown in FIG. 4, furthermore, a stepped portion 123 is formed at theupper end of the side walls of the housing 110 to engage with a thinwall 105 formed at the lower peripheral portion of the relay cover 101.The stepped portion 123 has a groove 124 which is filled with anadhesive to join the housing 110 and the relay cover 101. The groove 124further engages with projections 104 provided at the lower peripheraledge of the relay cover 101.

FIG. 5 is a perspective view showing the parts, which constitute therelay, in a disassembled manner. That is, the relay consists of ahousing assembly, into which the contact springs are insertion-molded,the electromagnet 116, which is inserted through the lower opening ofthe housing assembly, a back cover or bottom plate 140 and the relaycover 101, which is not shown here.

In the housing assembly, fixed contact terminals 111a, 111b, 112a, 112b,and moving contact-mounting terminals 113a, 113b are insertion-moldedinto the insulating material of the housing 110, as mentioned above.Moving contact springs 115a, 115b having the shape of a fork arespot-welded onto the moving contact-mounting terminals 113a, 113b.Contacts members 126a, 126b are attached to the upper surface of contactportions 112a", 112b" of the fixed contact terminals 112a, 112b, andcontact members, which are not shown, are also attached to the lowersurfaces of contact portions 111a", 111b" of the fixed contact terminals111a, 111b. Contact members 125a, 125b are welded onto the uppersurfaces of the forked portions of the moving contact springs 115a, 115bat positions opposed to the contact members of the fixed contactterminals 111a, 111b, and contact members, which are not shown, are alsowelded onto the lower surfaces of the forked portions at positionsopposed to the contact members 126a, 126b of the fixed contact terminals112a, 112b.

The electromagnet 116 (illustrated disassembled in FIG. 15A) comprises acoil bobbin 128, a coil 129 wound on the coil bobbin, a core 130, anearly L-shaped armature 117, and an armature-holding spring 118. Thecore 130 has a yoke 131 and a core portion 132, which is not shown inFIG. 5, but which is inserted in the coil bobbin 128; the core 130assumes a U-shape (as illustrated in FIG. 17) and is produced by amethod that will be mentioned later. Projections 132a, 132b are formedon both sides of the yoke 131. When the electromagnet 116 is inserted inthe housing 110, the projections 132a, 132b are fitted into the guidegrooves 127a, 127b formed in the opposing walls of the housing 110;i.e., the electromagnet 116 is placed in position in the housing. Theinsulator 120 is mounted on the tip portion of an arm 117' of theL-shaped armature 117, the tip portion being nearly parallel with theyoke 131 and being oriented in a direction at right angles with the axisof the arm, thereby maintaining electrical insulation between thearmature 117 and the moving contact springs 115a, 115b. Further, aprojection 135 is formed on the upper surface of the arm to engage withan opening 134 formed in a tip portion of the spring piece 133 of thearmature-holding spring 118. Recessed portions 136a, 136b are formed inthe outer side at the folded portion of the armature 117. Tongue pieces137a, 137b of the armature-holding spring 118 are engaged with therecessed portions 136a, 136b. The armature-holding spring 118 isinserted in grooves 139a, 139b formed in a flange 138 of the coil bobbin128. Coil terminals 119a, 119b are insertion-molded into the flange 138,and lead wires from the coil 129 are soldered to the upper ends of thecoil terminals 119a, 119b.

The back cover 140 has projections 140a, 140b that fit guide grooves127a, 127b of the housing 110, and notched portions 141a, 141b throughwhich coil terminals 119a, 119b of the electromagnet 116 are allowed topass.

To manufacture the relay using the above-mentioned parts, theelectromagnet 116 is inserted through the lower opening of the housingassembly, and the back cover 128 and the relay cover 101 are adhesivelyattached to the housing 110. Next, the whole relay is washed with awashing solution, and the protrusion 103 is cut off from the relay cover101 to form a ventilation port for releasing the heat. The relay is thusassembled.

Below is mentioned the operation of the relay. When the electromagnet116 is not excited, the arm 117' of armature 117 is pressed toward theyoke of the core 130 by the spring piece 133 of the armature-holdingspring 118, as will be obvious from FIGS. 3 through 5. Therefore, themoving contact springs 115a, 115b contact the fixed contact terminals112a, 112b on the breaking side due to their own resiliency. When theelectromagnet 116 is excited, another arm of the armature 117 isattracted by the core 132, whereby the arm 117' is pushed up against theforce of spring piece 133 of the armature-holding spring 118.Consequently, the moving contact springs 115a, 115b are pushed up viathe insulator 120, and come into electric contact with the fixedcontacts 111a, 111b on the making side, to switch the contacts.

Below is mentioned the method of producing parts which constitute therelay. The housing assembly is obtained by insertion-molding contactterminals into the housing 110, which comprises an elongated frame, asmentioned above. That is, two lead frames 150a, 150b, obtained from ahoop member of phosphor bronze by press working, are positioned oppositeeach other and separated by a predetermined distance, as shown in FIG.6. The lead frame 150a has fixed contact terminals 111a, 112a and movingcontact-mounting terminal 113a, and the lead frame 150b has fixedcontact terminals 111b, 112b and moving contact-mounting terminal 113b.Then, as shown in FIG. 7, the housing 110 is so molded as to contain theopposing terminals in the side walls; thus, the insertion-molded base isprepared.

FIG. 8 schematically illustrates the facility for insertion-molding theabove-mentioned housing assembly, in which the two lead frames 150a,150b are held by guide plates 151a, 151b positioned a predetermineddistance apart, and are moved in the direction of arrow A after eachpredetermined period of time by utilizing holes 152 formed in the upperand lower strap portions of the lead frames. In FIG. 8, the lead frames150a, 150b are reversely disposed relative to those of FIG. 6 withregard to the upper and lower directions, and right and left directions.In FIG. 8, therefore, the housing assemblies are formed upside down. Thelead frames 150a, 150b, positioned a predetermined distance apart, aresandwiched by outer shells 153a, 153b, and a core 154 is inserted intothe space between the lead frame 150a and the lead frame 150b from theupper direction, and a plate 155 for receiving the core 154 is placed inthe lower portion. A resin is then injected through a gate portion 156defined by the outer shells 153a, 153b. After the injected resin issolidified, the outer shells 153a, 153b, core 154 and plate 155 aremoved in the directions of arrows B, C, D and E, respectively. The leadframes 150a, 150b are then moved by a predetermined distance in thedirection of arrow A, and the next molding operation is executed. Thus,the insertion-molded base shown in FIG. 7 is produced continuously andautomatically.

The housing assembly is completed by removing the upper and lower strapportions from the lead frames 150a, 150b, folding at right angles theupper portions of the fixed contact terminals 111a, 112a, 111b, 112b andthe moving contact-mounting terminals 113a, 113b, welding the contactmembers to the fixed contact terminals, and spot-welding the movingcontact springs 115a, 115b to the moving contact-mounting terminals113a, 113b. It was mentioned that the contact members are welded afterthe upper portions of the fixed contact terminals were folded at rightangles. It is, however, possible to weld the contact members prior tofolding the upper portions of the fixed contact terminals at rightangles.

Here, it is desired to reduce the thickness of the housing 110 as muchas possible, to reduce the size of the electromagnet, and to minimizethe space required for mounting it. The arrangement of the contactterminals 111a, 112a, 113a and the like penetrating through the housing110, however, is limited by the construction of the electromagnet 116and by the standardized distance between the holes for mounting therelay. Therefore, the contact terminals are not often positioned in thecenter of the side walls of the housing 110. When the housing 110 isformed by molding, therefore, the contact terminals 111a, 112a, 113a,etc., which must be straight, as shown in FIG. 9, are often pushed bythe resinous material that flows into the thick side 110' of the housing110, and are bent toward the thin side 110" of the housing 110 as shownin FIG. 10. Consequently, central portions of the contact terminals111a, 112a, 113a, etc. are exposed to the inner side of the housing 110,and are often undesirably brought into contact with the electromagnet116 that is inserted in the housing 110. To cope with this problem, thehousing 110 may be formed while holding the central portions of theinserted parts (contact terminals 111a, 112a, 113a, 111b, 112b, 113b) bypins. With this method, however, holes are formed in the molded housingwhere the pins are inserted. Accordingly, the inserted parts areexposed, causing deterioration of the quality of the product, or anadditional operation is required to fill the holes. When small productsare to be molded, furthermore, pins are not often allowed to beintroduced into the metal mold to hold the inserted parts.

According to the present invention, as shown in FIGS. 11A and 11B,therefore, the contact lead terminals 111a through 113a of the leadframe 150a have projections 111a' through 113a' that protrude in apredetermined direction. The projections 111a' to 113a' each have threesides that are contiguous with the contact lead terminal member, and,further, have openings 171 through 173 through which the resinousmaterial is allowed to flow in the direction of arrow F during theoperation of insertion molding. Further, the contact lead terminals ofthe lead frame 150b, which are not shown, is provided with projectionsthat protrude in the direction opposite to the projections 111a' through113a'.

As shown in FIG. 12, therefore, if the lead frames 150a, 150b aredisposed in a symmetrical manner in the metal mold, which is not shown,to mold the resin housing 110, which contains the central broadenedportions of the contact lead terminals, the flow of the resin is dividedtoward the right and left directions of FIG. 12, owing to the openings171 through 173, and then meets at the rear side (back side in thedrawing) to fill the cavity in the metal mold. In this case, owing toprojections 111a' through 113a' protruding toward the thick side 110' ofthe housing 110 and owing to the openings 171 through 173, the resinousmaterial flows into the thick side 110' of the housing 110 and into thethin side 110" in nearly equal amounts compared to the lead frames ofthe conventional construction (denoted by 150a, 150b in FIG. 6).Furthermore, the pressure of the resinous material, which has passedthrough the openings 171 through 173, is elevated in the thin portion110". On the other hand, the pressure of the resin which flows into thethick side 110' is reduced as it passes through the projections 111a'through 113a'. The contact lead terminals 111a through 113a, therefore,are maintained straight.

As shown in FIGS. 13A and 13B, furthermore, the central broadenedportion of the lead terminal 113a may be provided with a projection113a" that forms an O-shaped opening 173', and the central broadenedportions of the lead terminals 111a and 112a may be provided withprojections 111a" and 112a" that form C-shaped openings 171', 172'. Theprojections 111a" to 113a" rise in the same directions, and are tiltedby about 45° toward the direction of arrow G in which the resinousmaterial flows.

As shown in FIG. 14, therefore, if the lead frames 150a, 150b aredisposed opposite each other in the metal mold, which is not shown, andif the resin housing 110 is molded so as to contain the centralbroadened portions of the lead terminals 111a through 113a and 111bthrough 113b, part of the resin, allowed to flow into the thick side110' of the housing 110, is guided by the projections 111a" through113a". The resin then flows through the openings 171' through 173' andflows into the thin side 110" of the housing 110, so that the cavity inthe metal mold is filled with the resin. In this case, the pressingforce of the resin flow, acting upon the projections 111a" through 113a"protruding toward the thick side 110', works to equalize the pressuredifferential of the resin created by the difference of the gap betweenthe thick portion 110' and the thin portion 110", whereby the leadterminals 111a through 113 a and the like are maintained straight.

Using lead frames constructed in this manner, therefore, it is possibleto insertion-mold thin plate-like insertion parts having littlemechanical strength without causing deformation thereof. Therefore, notonly can the proportion of defective molded products can be reduced, butalso molded products of a reduced thickness and a small size can berealized.

How the electromagnet 116 is assembled is described below with referenceto FIGS. 15A and 15B. In FIG. 15A, an accommodation portion havingprotruding walls 138a, 138b, which extend perpendicularly, is formed onone flange 138 of the coil bobbin on which the coil 129 of theelectromagnet 116 is wound, and grooves 139a, 139b, in which thearmature-holding spring 118 is inserted, and insertion holes 139a',139b', in which the coil terminals 119a, 119b are inserted, are formedin the walls 138a, 138b on the side remote from the flange surface. Toassemble the electromagnet, first, the coil terminals 119a, 119b areinserted and secured in the insertion holes 139a', 139b', the coil 129is wound on the coil bobbin 128, and lead wires of the coil 129 areconnected by soldering to the upper ends of the coil terminals 119a,119b. Then, the core portion 132 of the core 130 is firmly fitted intoan insertion hole 128' of the coil bobbin 128, to fasten the coil bobbin128 and the core 130 together. A corner 117' of the armature 117 isbrought into contact with an end 131a of the yoke 131, and thearmature-holding spring 118 is inserted into the grooves 139a, 139b ofthe coil bobbin 128. In this case, the opening 134 at the tip of springpiece 133 of the armature-holding spring 118 engages with the projection135 of the armature 117, and tongue pieces 137a, 137b of thearmature-holding spring 118 are engaged with recesses 136a, 136b of thearmature 117. Thus, the armature 117 is pressed onto an end portion 131aof the yoke 131, being urged by tongue pieces 137a, 137b of thearmature-holding spring 118, and is permitted to rotate with the end131a serving in lieu of a shaft. Here, the spring piece 133 of thearmature-holding spring 118 works to downwardly push the arm 117' of thearmature 117, i.e., it works to restore the armature 117. Further, theraised pieces 118a, 118b of the armature-holding spring 118 work toprevent the armature-holding spring 118 from being removed from thegrooves 139a, 139b of the flange 138. Thus, the electromagnet 116, whichis shown in FIG. 15B, is manufactured.

The core 130 employed for the electromagnet 116 is obtained by folding amagnetic member in a U-shape. As shown in FIGS. 16A and 16B, themagnetic member consists of a core portion 132' of a rectangular shapein cross section, which serves as the core 132, and a yoke portion 131'of a rectangular shape in cross section, which serves as the yoke 131.The core 132 and the yoke 131 have different widths and thicknesses.That is, the yoke portion 131' has a thickness D1, which is smaller thanthe thickness D2 of the core portion 132', making it possible to reducethe height of the relay and to obtain relays of more compact sizes. Theyoke portion 131', however, has a width W1, which is greater than thewidth W2 of the core portion 132', so that both portions 131' and 132'have nearly the same sectional area. The above-mentioned magnetic memberis folded at right angles at positions P1 and P2, indicated by chainlines in FIGS. 16A and 16B, in the directions indicated by arrows H andJ, and a U-shape core is formed as shown in FIG. 17.

When the magnetic member shown in FIGS. 16A and 16B is used, however,the thickness at the U-shaped bent portion 175 tends to be reduced, andthe sectional area of the core at this portion is reduced, causing thereluctance at this portion 175 to be increased. The increase in thereluctance, however, can be prevented by employing, for example, amagnetic member that is shown in FIGS. 18A and 18B. The magnetic membershown in FIGS. 18A and 18B consists of the yoke portion 131' and thecore portion 132'. Here, however, the portion of width W1 stretches intothe core portion 132', passing over the folding position P2. Further,tilted portions 176 are so provided that the thickness will not changesuddenly over the portion from the yoke portion 131' to the core portion132'. Therefore, the sectional area of the core in the vicinity of thefolding position P2 is greater than the sectional area of the yokeportion 131' or the core portion 132'. By folding the above-mentionedmagnetic member at positions P1 and P2 in the directions of arrows H andJ, the U-shaped core shown in FIG. 19 can be formed. In this case, sincethe thickness of the folding portion 177 around the folding position P2is swollen, the sectional area of the core does not become smaller thanthat of the yoke portion 131 or the core portion 132, even in theportion where the thickness changes from D1 to D2. In FIG. 18B, cutportions 178 are provided to decrease the sectional area of the broadportion around the folding position P2, so that the width of the core130 at the folding position P2 will not become greater than the width ofthe yoke portion 131. By using a magnetic member of the shape shown inFIGS. 18A and 18B, it is possible to maintain a uniform sectional areaof the core of the magnetic circuit from the yoke portion 131 of core130 to the core portion 132. Therefore, the reluctance is kept uniform,and the efficiency of the electromagnet is increased. Further, since apiece of the magnetic member is folded to obtain the core, no operationis required to fasten the core and the yoke together by caulking, whichwas required hitherto for assembling electromagnets.

What is claimed is:
 1. In an electromagnetic relay in which anelectromagnet assembly, having at least a core, a coil bobbin on which acoil is wound and an armature, is accommodated in a box-shaped insulatedhousing which has surrounding walls to hold fixed contact springterminals and moving contact spring terminals, the improvementcomprising:said insulated housing has upper and lower surfaces which areopen; said coil bobbin has a flange; said electromagnet assembly isincorporated into said insulated housing through the lower surfaceopening and includes accommodation means, having a portion that ismolded on the outer surface of the flange of said coil bobbin as aunitary structure, for rotatably holding said armature, with saidarmature and said core being supported by said coil bobbin; and saidelectromagnetic relay further comprises a bottom plate that is fitted tothe lower surface opening of said insulated housing and covers saidelectromagnet assembly.
 2. An electromagnetic relay according to claim1, wherein said core comprises a portion of a U-shaped unitarystructure, the core portion being inserted into said coil bobbin, saidU-shaped unitary structure further including a yoke portion that extendsalong the outer side of said coil bobbin, said yoke portion having awidth wider than that of said core portion, said yoke portion beingpositioned in said insulated housing to close the upper opening thereof.3. An electromagnetic relay according to claim 2, wherein said insulatedhousing includes protrusion means, extending from the upper portions ofthe opposing side walls of said housing at right angles with said sidewalls, for holding the electromagnet assembly.
 4. An electromagneticrelay according to claim 2, wherein said yoke portion of said core hasprojections at both side portions thereof, and said insulated housinghas, in the inner walls thereof, guide grooves that engage with saidprojections.
 5. An electromagnetic relay according to claim 1, furthercomprising a relay cover, made of an insulating material, covering theupper opening of said insulated housing, said relay cover having aprojection that can be removed from the outer side so that a ventilationhole is formed in the upper surface of the relay cover.
 6. Anelectromagnetic relay, comprising:a box-shaped insulated housing havingupper and lower surfaces which are open and surrounding walls holdingfixed and moving contact spring terminals; an electromagnet assemblyincorporated into said insulated housing through the lower surfaceopening, comprising:a coil bobbin having a flange having an outersurface at one end and a coil wound thereon; a U-shaped unitarystructure, supported by said coil bobbin, comprising:a core portion,inserted into said coil bobbin, having a first width; and a yokeportion, extending outside of said coil bobbin and positioned close tothe upper surface opening in said insulated housing, having a secondwidth wider than the first width; an armature having a generally L-shapeincluding a bent portion; and accommodation means for accommodating saidarmature, comprising:a portion molded onto the outer surface of theflange of said coil bobbin as a unitary structure; and armature-holdingspring means, affixed to the portion molded on the outer surface of theflange of said coil bobbin, for pressing the bent portion of saidarmature onto an edge of the yoke portion to rotatively support saidarmature.
 7. An electromagnetic relay according to claim 6, furthercomprising elongated moving contact springs affixed to said movingcontact spring terminals and extending over a portion of said armature,and an insulator attached to an end portion of said armature to insulatesaid moving contact springs from said armature.
 8. An electromagneticrelay according to claim 6, wherein said armature has recessed portionson the outer side of its bent portion, and said armature-holding springmeans includes tongue pieces that engage said recessed portions.
 9. Anelectromagnetic relay according to claim 6, wherein saidarmature-holding spring means includes a spring piece to push saidarmature toward said yoke portion.
 10. An electromagnetic relayaccording to claim 6, wherein said accommodation means includes a pairof coil terminals to which lead wires from said coil are connected. 11.An electromagnetic relay according to claim 1, wherein said fixedcontact spring terminals and moving contact spring terminals areinsertion-molded in the surrounding walls of said insulated housing. 12.An electromagnetic relay according to claim 11, wherein said fixedcontact spring terminals and moving contact spring terminals areinsertion-molded in the surrounding walls of said insulated housing atpositions offset with respect to the center of said walls.
 13. Anelectromagnetic relay, comprising:a box-shaped insulated housing havingsurrounding walls holding fixed and moving contact spring terminals,said fixed contact spring terminals and said moving contact springterminals being insertion-molded in the surrounding walls of saidinsulated housing and having projections embedded in the surroundingwalls of said insulated housing, the projections protruding toward theside of the surrounding walls that is farthest from the fixed and movingcontact spring terminals, the projections having openings to divertinsulation material toward the side of the surrounding walls that isclosest to the fixed and moving contact spring terminals, during theinsertion molding; and an electromagnet assembly, enclosed by saidbox-shaped insulated housing, comprising:a coil bobbin having a flangewith an outer surface at one end and a coil wound thereon; an armature;accommodation means, having a portion molded on the outer surface of theflange of said coil bobbin as a unitary structure, for rotatably holdingsaid armature; and a core supported by said coil bobbin.
 14. Anelectromagnetic relay according to claim 12, wherein said fixed contactspring terminals and said moving contact spring terminals have foldedpieces at portions that are embedded in the surrounding walls of saidinsulated housing, said folded pieces protruding toward the side of saidwalls that is farthest from said terminals, said folded pieces beingfolded in a direction that diverts part of the flow of the insulationmaterial toward the side of said walls that is closest to said terminalsduring insertion molding.
 15. An electromagnetic relay, comprising:anelongated bobbin element having a first end, a second end, and a cavityregion adjacent the second end; a coil wound on said bobbin elementbetween said first end and an intermediate position between said firstand second ends; a generally L-shaped armature disposed adjacent saidcoil, said armature having a first leg extending into said cavity regionand a second elongated leg extending toward the first end of said bobbinelement, said first and second legs intersecting at a bent portion ofsaid armature; means mounted on said bobbin element and extending intothe bent portion of said armature for rotatably supporting saidarmature; and spring means, affixed to said bobbin element adjacent thesecond end thereof, for biassing said first leg of said armature towardsaid bobbin element.
 16. The relay of claim 15, wherein said bobbinelement has an elongated additional cavity extending from the first endof said bobbin element to the cavity region adjacent the second end, andwherein said means for rotatably supporting said armature comprises agenerally U-shaped piece having a first elongated arm that is insertedinto said additional cavity and a second elongated arm extending betweenthe coil and the first leg of the armature, the second arm terminatingin an edge that is substantially perpendicular to the axis of saidbobbin element, said edge extending into the bent portion of saidarmature to rotatably support said armature.
 17. The relay of claim 16,wherein the cross-sectional area of said U-shaped piece is substantiallyconstant along the first arm, second arm, and portion joining the firstand second arms.
 18. The relay of claim 17, wherein said spring meanscomprises a spring element having an anchor portion lodged in groovesprovided on said bobbin element adjacent the second end thereof and anelongated tongue portion pressing against the second leg of saidarmature.
 19. The relay of claim 18, further comprising a housing havingterminal elements molded in the walls thereof, and an elongated springcontact affixed to one of said terminals, said spring contact extendingsubstantially parallel to said second leg of said armature.